Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.
Known overflow launders include catchment troughs which surround the outer perimeter of a separation cell. A separation cell is typically a device for separating particles via the use of a fluid or which is typically a liquid but which may be a gas. The precise basis of the separation is not important. In flotation processes, the separation may be achieved via the attachment of hydrophobic particles to rising air bubbles. In a fluidised bed classifier the separation may arise through the entrainment of slower settling particles with the upward flowing fluid, and in thickening the separation is achieved by ensuring that virtually all of the solid particles segregate from the upward fluid flow. The fluid and any entrained particles or bubbles, for example, then overflows into the trough or launder.
A disadvantage of having the catchment trough around the perimeter of the cell is that particles entrained by the upward flowing fluid must travel laterally with a substantial horizontal motion near the surface of the vessel in order to reach the rim of the separation cell, unless of course they originate from a location near the vessel perimeter. It is during this substantially horizontal motion near the surface of the vessel that there is a possibility that a particle may separate from the overflow and fall back towards the base of the cell. This is inefficient as the particle must again undergo a separation process so that it can finally reach the rim.
In some vessels an internal launder is also provided, typically in the form of an inner annulus or trough, but upwardly flowing fluid must still travel laterally a significant distance with a substantially horizontal motion near the surface of the vessel in order to reach either the internal launder, or the outer trough.
Further disadvantages occur when using overflow launders with a reflux classifier, which is a separate cell that includes a series of inclined parallel plates that allow particular particles to rise to the surface, which may depend on the properties of the particles such as their size or density. When using the above overflow launder in conjunction with the reflux classifier, there can be a tendency for particles to become segregated from the overflow, and hence a tendency for these particles to re-enter the inclined channels at a position closer to the overflow perimeter. This may produce a downward flow in an included channel or even a blockage. A downward flow is associated with internal interactions between different channels. This internal flow circulation may produce higher upward flows in some channels, and downward flows in other channels, or even upward or downward flows in the same channel. This interaction may then produce a poorer quality separation.
It is an objective of the present invention to overcome or ameliorate at least one or more of the disadvantages of the prior art, or at least to provide a useful alternative.